LARS: COULD YOU POST AN ARTICLE ON SETTING TOTAL TIMING FOR MY 502. MANUAL SAYS 14 AT 900 RPM, BUT ID LIKE TO SET IT LIKE YOU STATED IN AN EARLIER POST FOR A SMALL BLOCK

 

TTT

 

Melvin -
The BB can be set up just like the SB for total timing of 36 at 2500 rpm. The paper I have on setting the timing is not specifically for the SB - it applies to all GM V8's. I'll copy and paste the text of the paper here for those who haven't seen it:

How to Set Your Timing for Peak Performance
(Non-HEI)

by Lars Grimsrud
SVE Automotive Restoration
Musclecar, Collector & Exotic Auto Repair & Restoration
Broomfield, CO Rev. B 4-18-01


This tech paper will discuss setting the timing on a Chevy V8. This procedure also applies to other GM V8s.

The procedure outlined here differs from the Service Manual, and is based on my years of experience doing this work in the quickest, least painful, most economical way while keeping the level of quality high. It is recognized that other people will have different methods of doing things, and may disagree with specific methods and procedures that I use.

How to Set the Timing
When you think about it, setting the timing at idle speed makes no sense at all: You don't operate your car at idle, and timing changes as the rpm changes. Fact is, the timing spec at idle speed is provided as a simple way for most people to set the timing, and is not a good procedure for optimum performance.
Small block Chevys (and most other GM performance V8 engines) perform best when the total timing (full centrifugal advance plus the initial timing setting with vacuum advance disconnected) is all in by 2,500 - 2,800 rpm and is set to 36 - 38 degrees. If you have an adjustable timing light, this is very easy to check. If you don't, you need to scribe a 36-degree mark on your harmonic balancer. Here's how:
Measure the circumference of your harmonic balancer using a sewing tape measure (or other flexible tape measure). Get it as accurate as you can. Take this measurement and divide by 10. The number you get is the distance to 36 degrees. Measure this distance CLOCKWISE from your existing harmonic balancer timing mark and place a clear mark on the balancer.
Remove your distributor cap and rotor. Remove the 2 centrifugal advance springs. Install the rotor and the cap (without the springs). Disconnect the vacuum advance.

NOTE: This procedure cannot be used on the HEI ignition systems. Removal of the springs will cause an artificially over-advanced condition that will never be achieved with the springs in place. You can use the basic technique described in this paper with the HEI units (setting timing up to 36 degrees), but to check total timing, you must install a set of soft springs. You cannot remove the springs altogether. With the soft springs in place, rev the engine until the centrifugal advance is pegged out. Adjust for 36 degrees total. Then re-install your original springs.

Start the engine. It may kick back a little due to the advance coming in immediately without the springs. If you're using an adjustable timing light, set the light to 36 degrees advanced. Now rev the engine just a little while observing the timing marks with the light. It shouldn't take much rpm to peg out the advance without the springs installed. With an adjustable light set at 36 degrees, align the stock timing marks with "0" when the timing is "pegged out." With the non-adjustable light, align your new 36-degree mark with "0." Rev the engine a little to make sure the timing will not advance any further. Shut it down.
Pop the cap and rotor and re-install the springs. Put everything back together, but leave the vacuum disconnected. Start it up. For future reference, make a note of the timing setting at idle. This is your new curb idle timing spec. Now give the engine a few quick rev's past 3,000 rpm and verify that the full timing (36 degrees) is coming in. If it's not, you need to change to a softer set of springs until you get full 36-degree advance before 3000 rpm. (NOTE: A stock set of springs will usually not allow full centrifugal advance to come in before redline rpm. If you have stock springs installed, don't rev the engine beyond its limits to try to force full advance in.)
Shut it down and hook up the vacuum. Now do a road test.
The 36-degree 2500 rpm advance curve is optimum for performance, but may require premium fuel. Lug the car around, and punch the throttle at low rpm while listening for detonation ("engine knock"). If you're getting any audible knock, you MUST retard the timing. Retard the timing in 2-degree increments until engine knock stops. Engine knock will seriously damage engine components if not corrected. If you get no knock, you may see slightly improved performance at 38 degrees total timing. This is particularly true if you're running at high altitude.
If you have no engine knock under acceleration, but the car "chugs" or "jerks" at cruising speed (light throttle application), you are getting too much vacuum advance on top of the mechanical advance. You may need to change out the vacuum advance diaphragm with an adjustable unit available from aftermarket sources. Adjust these units so that you get the most vacuum advance possible without any "chugging" or "jerking" at cruise speed.
Your timing is now set for best possible performance. Make note of the new setting, and use this for your future tune-up work.

Questions, Comments & Technical Assistance
If you have questions or comments regarding this article, or if you notice any errors that need to be corrected (which is quite possible since I'm writing this from memory…), please feel free to drop me an e-mail. Also, if you need any technical assistance or advice regarding this process, or other maintenance issues, feel free to contact me:

lars.grimsrud@lmco.com

 

Lars, What about those of us with HEI??? And how is the HEI different?
Thanks from all of us for your help!!!!!
Mike

 

Yes, should those of us with HEI set the timing to 36 and 2800 RPM with the advance unhooked or with the advance hooked up or what?

 

Mike -
The paper discusses the HEI method: Don't remove your springs, but rather install a random set of very soft springs so your full centrifugal slams in at a moderate rpm so you can safely observe it (buy a Mr. Gasket part number 928. This is an advance kit for a non-HEI distributor, but the springs work great. Use the two gold springs out of the kit). The HEI is different due to the geometry of the stock weights. Removal of the springs causes an over-advanced condition that does not occur at any rpm with the springs in place.

 

Dala -
Regardless of the type of ignition system in use (points, Pertronix, MSD, HEI, whatever..) always set up total mechanical timing with the vacuum advance disconnected. The vac advance merely provides a compliment to the mechanical curve when the car is at cruise. It provides a variable advance based on engine load, so we disable and disregard the vac advance when setting up total mechanical timing. I have a separate paper regarding vac advance theory and application if you'd like to do a little reading... e-mail me for a copy.

 

For those of us stuck with the computer controlled HEI, do you do the same thing with the ECM lead unplugged? No springs, so how does that effect the readings?

 

Chris -
The ECM-Controlled systems cannot be set up and tweaked in this fashion. Since there are no advance springs and no vacuum advance, the entire ignition curve is controlled by the ECM. The aftermarket "chips" do exactly what we do with the curve kits and springs on the earlier cars: get a quick, aggressive curve in with a 36-degree total under power. So you're stuck with playing with the electronics and the programming... the others have to play with springs and weights...

 

This being the case, can you check the total timing the chip is providing by leaving the ECM hooked up? Mine has the Hypertech chip (Stage 2), but I have no idea what it was programmed to do for timing. I called them one time and the guy I talked to didn't know and wasn't going to take the time to check. :smash:

 

Thanks Lars!!! I will try this out. I have my L 82 at 14 degrees now on the balancer and it runs great. I'm interested to see what the total will be doing it the "right" way. Again, thanks for all the help!
Mike

 

Lars, is a patient man.

Let me ask this one for those of us with a Mallory Unilite distributor with mechanical advance (there is no provision for vacuum advance).(Mallory makes a kit to adjust total advance). The specs on this dist say total advance is approx 24-28 I believe. I assume this would not include any "initial" advance. The Mallory tech said it should be fine right out of the box for most stock to mildly cammed engines.

My question is, should this be treated the same as a non-HEI dist.?? And also, when you get the advance properly set what does that do to the performance characteristics of the car?

Thanks again (and again),Lars.

Regards, mark :flag :chevy

 

Chris -
Geez, that sounds about like the type of tech support you get from places anymore. That really frosts me when they sell you stuff and don't provide diddly for tech.

Your ECM-controlled ignition can be readily observed if you have an adjustable timing light. Make sure the car is fully warmed up so it's in the "closed loop" (computer-controlled) mode. You can then raise the rpm and watch the advance curve take off as the ECM advances the timing for the no-load condition at elevated rpm. It's pretty cool to watch while thinking about that it's the computer that's doing the full control of the timing adance. Under load, the ECM will run the timing up to the point that the knock sensor detects detonation, then back it off a touch. One of the really cool things about your ECM-controlled car is that if you put premium gas in it, the ECM can advance the timing further before the knock sensor goes off. Thus, the car will actually produce more power and be quicker if you put higher octane fuel in it. The rest of us are stuck with whatever total timing we set the car up for.

MikeT -
14 degrees initial is probably going to get you awfully darned close, actually. The guys that really benefit are those who set the timing up to the 8-10 degree initial spec: this is typically far short of optimum.

Mark -
Hi! Good hearing from you!
The Mallory with the non-vacuum advance should likewise be set up for 36 max total. Total, as I see you know, is the initial timing plus the amount of centrifugal timing that the distributor centrifugal advance mechanism will produce as rpm comes up. If your distributor is dialed in to produce "24 degrees advance," this means that it will produce 24 degrees of centrifugal advance on top of whatever initial timing you set it at. This, if you set your initial at 12 degrees, you'll end up with a perfect 36-degree total "right out of the box."

I have not played much with the Mallorys, so I cannot attest to the technique of removing the springs. However, the Mallory should be set up with a perfrmance curve to it, so you should be able to see the total max timing simply by revving the engine in neutral briefly up past 2500 - 3000 rpm. If the timing stops and doesn't advance any more, you've hit the max advance.

A properly set advance consists of two things: Getting the optimum maximum timing to occur at the correct rpm, and getting the max timing set to the right point. Experience tells us that GM V8 engines, including our BBs and SBs, will produce peak power when the total max timing is set in a range of 34-38 degrees (more at higher elevations). Light cars respond well when this total max comes in at a fairly low rpm (below 2500). Heavier cars prefer this total max timing to come in a little later, say 3000 - 3500. When the timing is set up to these optimum specs, you will achieve noticably better throttle response both off-idle and at part-throttle cruise. You can measure improvements in higher 1/4-mile mph when the timing is at its optimum. Overall, the car will simply feel much more responsive when this is correctly set up.



My question is, should this be treated the same as a non-HEI dist.?? And also, when you get the
advance properly set what does that do to the performance characteristics of the car?

Thanks again (and again),Lars.

 

Hey Lars I have benefited previously from your great advice but I had a question. I just installed an MSD tach drive distributor in my 502 big block and was wondering about my setup. Currently I have the smallest bushing installed which allows 28 degrees of advance and the lightest springs which brings max advance in by 2300 rpm according to spec although I have not verified it. So given these specs I am running 8 degrees initial for the total of 36 ar 2300 rpm. The car seems to run great. My question is would there be any benefit to running a smaller advance bushing say the 24 and running more initial timing of say 12 or more with the smallest bushing or does it not matter as long as its in early. Thanks Lars.

 

Here's a good test to see what you need for initial: Simply loosen up the distributor at idle and start twisting it one way and the other very slowly. Don't touch or use a timing light. Turn the distributor until the engine has the best quality - not necessarily FASTEST - idle: smoothest and best idle quality. Once you find the sweet spot, throw the timing light on it and see where the initial timing ends up. It will probably be in the 12-14 degree range, but could be a lot higher depending on how "bad" your cam is. With this number determined, select the bushing that will then get you the number of centrifugal advance degrees to get you up to 36 total.

Set up like this, you will end up with some great off-idle throttle response with matching awesome high-rpm power. If it doesn't work for you, get the initial up to about 12 and select a bushing that will give you 24 centrifugal to give your low-rpm throttle response a boost.

Tag me back with any questions.

 

LARS: IM CLUELESS ABOUT THE "BUSHING"

 

Melvin -
The MSD aftermarket distributors use a special set of bushings to control/limit the centrifugal advance. By changing bushings, you can change the length of the advance curve. Stock distributors do not utilize such a system, so this does not apply to your setup. If you need to change the length of your advance curve, you have to do it by filing and changing the shapes of some of the mechanism parts.

 

Lars once again I am humbled by your knowledge. Thanks again and I will give this a shot tomorrow,and will let you know what I find out.

 

MELVIN.... if I remember correctly... you bought a new "replacement" OEM type points distributor.

It should have a bushing... GM calls it a sleeve...

view V2-32, item #7, group 2.385

It was originally made out of rubber, and is no longer available.
I replace them with brass (or bronze) from a Mr Gasket curve kit when they are toast.

Yours should be intact.... but in order to remove it... the distributor must be disassembled.
The distributor gear must be removed and the main shaft must be raised enough for the pin &
bushing to clear the slot in the cam plate.
This "bushing" rides in a slot in the cam plate and limits advance.

I would guess that this is beyond the scope of what you need/want to do.

Tom

 

The aftermarket distributor 69t is running is specifically designed to accomodate swapping out the supplied bushings in order to change the curve length. It's a pretty simple process, and completely different from the stock units. The stock replacement units, as Tom states, also have an advance stop bushing in them, but it is not designed to be swapped out with different sized bushings: it is pressed onto the stop pin, and you have to disassemble the distributor to get to it. On this type of distributor, you can change the length of your advance curve by changing the length of the slot that the bushing rides in: I shorten the slots (thereby shortening the curve) by welding material into the slot and machining it back down to the length I desire. I lengthen the slot (and lengthen the curve) by machining the slot a little longer, all the while retaining the available brass bushing pressed onto the pin.